1. Field of the Invention
Movement of molten metal in a mass or pool of molten metal in a metal-melting furnace, establishing and maintaining efficient circulation of molten metal therein, movement of said molten metal from a hotter area to a colder area and thereby enhancing the efficient melting of metal chips in the molten metal mass or pool.
According to the present invention, the conveyance of the molten metal is effected with simultaneous degassing of the melt by virtue of the introduction of the inert gas into the molten metal mass at a supersonic velocity through one or more nozzles or exit ports as will be further explained hereinafter.
2. Prior Art
For the efficient melting of metal chips, especially scrap metal chips, particularly brass, aluminum, magnesium, titanium, and alloys thereof, by introduction of the same into a pool or mass of molten metal, usually the metal of which they are formed or an alloy thereof, as in the feed or charge well of a metal-melting furnace, e.g., a reverberatory furnace or the like, it is not only desirable but necessary to circulate molten metal from the hottest area of the metal-melting furnace, that is, the main chamber thereof, out into side chambers or wells, and especially into the feed or charge well, on a continuous basis. According to present practice of the art, a molten metal circulating pump, fabricated at least partially of graphite, is the means of choice. Such a pump comprises a submerged discharge scroll which houses an impeller mounted on a vertical shaft which rides in silicon carbide bearings. The shaft, upon which the pump impeller is mounted, is driven by an air or electric motor located atop the pump several feet above the molten metal bath or pool. An alternate use for the same type of pump is to elevate molten metal above the level of the molten metal bath or pool for transfer into other containers, such as a refractory-lined ladle or into a trough which is covered and sometimes heated, referred to in the trade as a "launder". Such a device is also employed to transfer molten metal from one furnace to another. Inasmuch as graphite is refractory, i.e., heat-stable and resistant to attack by most metal alloys as well as characterized by good non-wetting characteristics, such graphite metal circulating pumps have broad acceptance in the metal melting and reclaiming industry. However, due to the fragile nature of the graphite parts, the close tolerance of the pump parts, and the frequent requirement of pulling the pump for cleaning, the wear and breakage expenses account for very high maintenance costs, which on an annual basis often exceed twice the initial cost of the pump. Accordingly, the search for improvements in the molten metal circulating pump design and in general for some means of transporting or conveying molten metal from one place to another, especially in a molten metal bath or pool in a metal-melting furnace, has had high priority. Despite the efforts to date, no effective means or method for moving or conveying molten metal from one place to another, especially in a molten metal bath or pool in a metal-melting furnace, have been devised, despite a long-standing need for the same in the industry.
Moreover, in order to produce acceptable quality metal, e.g., aluminum, from remelted scrap, it is necessary to control the percentage of hydrogen gas in the alloy. Current practice uses a rapidly-turning rotor to disperse an inert gas, e.g., nitrogen gas, which is piped to the device rotating in the metal. The inert gas, e.g., nitrogen, gas bubbles help to remove hydrogen from the molten metal. Another method currently used is to bubble an inert gas, e.g., nitrogen, into a ladle filled with molten metal. The use of a spinning gas dispersal rotor is an improvement upon the simple bubble tube or lance. The disadvantage of the dispersal rotor is that the rotor will erode while in contact with the molten metal, and the small dispersing apertures will clog. The present invention, wherein molten metal is conveyed from one place to another in a metal-melting furnace with simultaneous degassing of the melt, represents a considerably advantageous improvement in the degassing art as well.